Color lake



Patented Oct. 4, 1932 UNHTED STATES REINI-IARD IBUCHWALD, OF LUDWIGSHAFEN-oN-THE REIlNE, GERMANY, ASSIG-NOR PATENT "or-rice T0 GENERAL ANILIN WORKS, inc; on NEW YORK, n. A CORPORATION on DELAWARE COLOR LAKE No Drawing. Application filed August 26, 1931, Serial No. 559,495, and in Germany September 5, 1930.

The present invention relates to improvements in the production of color lakes of dyeleuco compound of a basic dyestufiof the triand sodium bichromate.

the color lakes of the leuco compounds may be arylmethane series, which may also contain acid groups, with a solution of a complex inorganic acid selected from the group consisting of phosphotungstic acid, phosphomolybdie acid and phosphotungsticmolybdic acidv in the absence of agents capable of oxidizing leuco compounds of basic dyestuffs to the cor-' responding dyestuffs. Reduced complex acids may be employed for the precipitation as well as mixtures of the components capable of forming the said inorganic complex acids. During precipitation the solution is kept acid to an extent sufficient to dissolve at least a substantial amount of the leuco compound either by the employment of the complex acids in the free state or in the form of their acid salts, or by the addition of other, preferably strong, acids. Acids which may be used to dissolve the leuco compound comprise, for example, formic acid, oxalic acid, chloroacetic acid or a strong mineral acid, such as hydrochloric acid and sulphuric acid. The resulting color lakes of leuco compounds are then converted into the corresponding color lakes by oxidation either after isolation or immediately in the suspension obtained by the precipitation of the leuco bases with the said complex acids. Suitable oxidizing agents are for example hydrogen peroxide, arsenic acid,ferric oxide hydrate, chloran- 11, lead dioxide, potassium permanganate The oxidation of carried out at ordinary or elevated temperatures, for example while boiling, and at atmospheric or increased pressure. The oxidation may also be carried outin the presence of one of the substrata usual in the color lake Weight.

industry, or with an addition of dispersing agents, such as salts of alkylated naphthalenesulphonic acids, sodium cholate-and products of the type of Turkey red oils. The

color lakes obtained have greater brilliance and fastness to light than the color lakes produced by precipitating the. leuco compounds ofthe dyestuffs with complex acids and simultaneously oxidizing them. i

V The following examples will-further illustrate how the said invention may becarried out in practice, but the invention is not restrlcted to these examples. The parts are by i Ewample 1 I 800 parts of a 10 per cent solution of sochum phosphotungsticmolybdate are added at about C. while stirring well to 500 parts of a 10 per cent hydrochloric acid solution of the leuco compound of methyl green (Colour Index No. 684). The color lake of the leuco compound pf methyl green and phosphotu'ngsticmolybdic acid is precipitated in the form of a pale grey flocculent precipitate. "While stirring well, the resulting precipitate is oxidized'by the addition of 12 parts of a 5 per cent solution of poture is boiled fora short time by passing steam therethrough. The resulting color lake is'filtered oil", thoroughly washed and worked up in the usual manner.

.tas'sium permanganate. Finally the mixtassium'pe'rmanganate and a small amount ofhydrochloric acid are addedwhile stirring vigorously, the acid being added in-order ture the mixture is boiled for a short time with steam. After filtering the product is washed Welland dried.

1.2 parts of a per cent solution of potassium permanganate are added and vigorous stirring is continued. for about 1% hours at room temperature. The mixture is finally boiled-for a short time by passing steam therethrough. The resulting color lake is' filtered ofl' and washed well.

Eazample 4 200 parts of a per cent aqueous solution of the sodium salt of phosphotungsticmolybdic acid to which 0.2 part of diisopropylnaphthalenesulphonic acid has been added, are added to 220 parts of a5 per cent solution of the leuco base of Acronol brilliant blue (Colour Index No. 664) which has been made slightly acid by. the addition of sulphuric acid. The color lake of the said leuco base is thus precipitated. It is then oxidized to the color lake proper by the addition of parts of a 10 per cent solution of sodium bichromate while thoroughly stirring. The Whole is then' slowly heated to between 90 and 95 C. until the oxidation is complete. The color lake thus obtained is filtered o-fi, thoroughly washed and worked up in the usual manner.

Example 200 parts of a 2 per cent solution of the leuco base of diamond green G (Colour Index No. 662) which has been made slightly acid by means of sulphuric acid, are mixed With 0.2 part of the diisopropyl-naphthalenesulphonic acid, and then 40 parts of a 10 per cent solution of sodium phosphotungsticmolybdate are added. The color lake of the said leuco base is thus. precipitated. A well-washed substratum prepared from 20 parts of heavy spar, 10 parts of aluminium sulphate, 5 parts of calcined soda and 12 parts of barium chloride is then added to the reaction mixture. The color lake is then oxidized by the addition of 25 parts of a 5 per cent aqueous solution of potassium permanganate. By the oxidation, the color lake of diamond green G and the said complex inorganic acid is formed. After stirring 'for about hour the reaction mixture is boiled for. some time by passing steam throughit and'it is then worked up in the usual-manner.

What I claim is:

A process of producing color lakes which comprises precipitating a leuco compound of a basic dyestufl of the triarylmethane series with a solution of a complex inorganic acid selected from the group consisting of phosphomolybdic acid, phosphotungstic acid and 'phosphotungsticmolybdic acid, in the absence of agents capable of oxidizing leuco compounds of basic dyestuffs to the corresponding idyestufls, while keeping the reac-i tion mixture acid to anextent to dissolve at least a substantial amount of tl'ieleucocompound, and then oxidizing the color lake of the leuco compound to the color lake of the corresponding dyestufi." 1 i In testimony whereof I have hereunto set my hand.

REINHARD BUCHWALD. 

